Only one way to learn, Grasshopper. Try it yourself, and if you screw it up, you are no worse off.
$300 is butt rape for changing a seal. Ask around locally, and I guarantee there is a shade tree somewhere that would do it for less than half that.
Wynona loved her big brown beaver
And she stroked him all the time.
She pricked her finger one day and it
Occurred to her she might have a porcupine